how do u know if a backup works

[RincewindTheWiz]

If you have an exact backup, it will work forever. However for the securom new games, a method of copying was developed that allows you to use it as a backup, but the backup isn't an exact copy. So in future updates the copy protection could kick back in. What you probably heard about was FADE from Operation Flashpoint. This is an extra copy protection that kicks in when you try to play online with an invalid cd key. These two are about the only examples of degrading play I can think of.